In the present disclosure, the term high precision positioning is used to denote positioning methods that have a potential to meet the North-American E-911 emergency positioning requirements. Methods that meet these requirements are capable of obtaining positioning accuracies of                either (terminal based) 50 meters (67%) and 150 m (95%),        or (network based) 100 meters (67%) and 300 m (95%).        
One well-known positioning method is the so-called Assisted GPS (A-GPS) positioning method. A-GPS is an enhancement of the global positioning system (GPS). An example of an A-GPS positioning system is displayed in FIG. 1, in this case a WCDMA system. In this system, the radio network controller (RNC) acts as the node that collects, refines and distributes assistance data to the terminals (denoted user equipment (UE) in WCDMA). The core network (CN) requests positioning of a UE over the RANAP interface. In response, the RNC may use various kinds of A-GPS techniques, all these techniques do however build on assistance data being handled by a node in the cellular communication system. The RNC orders positioning measurements to be performed in the UE, measurements that are performed by dedicated A-GPS receiver hardware in the terminals. These receivers detect GPS transmissions from the satellites that are also denoted space vehicles (SVs).
Accordingly, the GPS reference receivers attached to e.g. a cellular communication system collect assistance data that, when transmitted to GPS receivers in terminals connected to the cellular communication system, enhance the performance [8] of the GPS terminal receivers. Typically, A-GPS accuracy can become as good as 10 meters also without differential operation. The accuracy becomes worse in dense urban areas and indoors, where the sensitivity is often not high enough for detection of the very weak signals from the GPS satellites.
Additional assistance data is collected from the cellular communication system directly, typically to obtain a rough initial estimate of the position of the terminal together with a corresponding uncertainty of the initial estimate. This position is often given by a cell identity (cell-ID) positioning step, i.e. the position of the terminal is determined with cell granularity. Alternatively, a more accurate position can be obtained by round trip time (RTT) positioning and/or soft(er) handover maps. The GPS time is also estimated with as good accuracy as the cellular system allows.
A recent development that exploits A-GPS is so-called Adaptive Enhanced Cell Identity (AECID) positioning [1]-[6]. A block diagram of an example of a basic implementation of the AECID positioning method is illustrated in FIG. 2.
The AECID positioning algorithm is based on a polygon format and an algorithm for computation of a polygon [7] from a cluster of tagged high-precision position measurements. In WCDMA the high precision measurements are e.g. being provided by A-GPS positioning steps. The main steps of the AECID algorithm are according to the schematic flow below (for WCDMA in particular steps 1a-1c, and steps 5ai-5aiii are important)                1. Tagging of high precision position measurements (e.g. A-GPS measurements) with at least one of                    a. Cell Ids of detected cells.            b. Auxiliary connection information (e.g. RAB, time)            c. Quantized auxiliary measurements (e.g. pathloss, signal strength, RTT, pre-coding indices (in multi-input-multi-output (MIMO) configurations these carry angular information) or noise rise)                        2. Collection of all high precision measurements with the same tag in high precision measurement clusters.        3. Calculation of a (tagged) polygon that contains a pre-specified fraction of said clustered high precision position measurements in the interior, thereby providing a polygon with known confidence [7] value. Note: The confidence is the probability that the UE is actually located in the reported region.        4. Storage of said tagged polygons in a database of polygons.        5. When an AECID positioning is to be performed, the following steps are performed:                    a. Determination of at least one of                            i. Cell Ids of detected cells.                ii. Auxiliary connection information                iii. Quantized auxiliary measurements                                    b. Formation of the tag, defined by step a.            c. Retrieval of the polygon, corresponding to said tag.            d. Reporting of said polygon, over RANAP or PCAP.                        
In order to provide reliable positioning according to the above described AECID method e.g. accuracy of the calculated polygons, it is necessary to gather a sufficient number of high-precision measurements in each cluster or for each tag. An insufficient number of measurements may result in a failed positioning or a low accuracy positioning. This leads to an increased waiting time before accurate positioning can be performed. Therefore, there is a need for a method of reducing the waiting time and provide accurate positioning when the number of high-precision measurements is below a certain threshold.